Road milling, mining, and trenching equipment utilizes bit assemblies having a bit and a base block. A bit tip insert is retained by the bit and the bit is retained within a bore in the base block. A plurality of the bit assemblies are mounted on the outside of a rotatable drum, typically in a V-shaped or spiral configuration. The combinations of bit assemblies have been utilized to remove material from the terra firma, such as degrading the surface of the earth, minerals, cement, concrete, macadam or asphalt pavement. Individual bits and base blocks may wear down or break over time due to the harsh road degrading environment. Additionally, the forces and vibrations exerted on the bit assemblies may cause the bit to wear away the bore of the base block. As a result, the diameter of the bore of the base block increases over time, decreasing the interference contact between the bit and the bore of the base block, damaging the base block, and requiring replacement of the base block long before the standard minimum lifetime required by the industry. To prolong the life of the bit assembly, and the base block, a bit comprising a diametrically expanding retainer circumferentially disposed around the shank of the bit is provided to maintain the interference contact between the bit and the bore of the base block as the diameter of the bore of the base block increases from use.